Electrorefining of impure anode copper to produce high purity copper cathode is a well known commercial process. As is known, in carrying out the electrorefining process, copper in the anode dissolves and reports at the cathode while insoluble impurities in the anode copper such as selenides, silver and precious metals during dissolution of the copper anode settle to the bottom of the electrorefining tank. Soluble impurities dissolve, of course, in the electrolyte, gradually building up in concentration. The most common soluble impurities are antimony, arsenic and nickel. Copper, however, also builds up in the electrolyte as a result of the dissolution of the copper oxide present in the anode copper. The copper oxide dissolves as is shown in Equation 1. EQU Cu.sub.2 O+H.sub.2 SO.sub.4 .fwdarw.CuSO.sub.4 +Cu+H.sub.2 O (Eq. 1)
To maintain a desirable copper concentration and reject impurities, a portion of the electrolyte employed in the electrorefining step is withdrawn and pumped to decopperizing cells or liberators. Indeed, these liberators typically consist of a number of cells to which the refinery electrolyte is passed in a cascaded series. In any event, the copper content of the solution passing through the liberators ultimately is depleted to such significantly low levels that the deposition potential of the copper becomes increasingly more positive resulting first in the generation of hydrogen within the cell and the concurrent deposition of the impurity metals, e.g., arsenic, antimony, bismuth and the like. Most importantly, however, the antimony and arsenic can thereafter be reduced to their respective hydrides, namely, arsine and stibine, which are extremely toxic gases, the evolution of which must be avoided.
A number of techniques have been disclosed for avoiding the evolution of arsine and stibine during operation of the liberator cells. For example, in U.S. Pat. No. 4,115,512, a method is described for removing arsenic from refinery electrolyte by solvent extraction. In U.S. Pat. No. 4,083,761, the application of periodic reverse current during operation of a liberator cell is disclosed as a technique for inhibiting arsine formation.
Now it has been discovered that in electrorefining processes, after partial decopperization of the electrorefining electrolyte, further decopperization of the electrolyte can be achieved by use of a fuel fed porous catalytic anode whereby the formation of toxic gases, such as arsine and stibine, are avoided.